1. Field of the Invention
This invention relates to a fluidized bed polymerization apparatus and an olefin polymerization process by using this apparatus, more especially, to a fluidized bed polymerization apparatus, with which an olefin polymer can be produced continuously for along period of time, stably and reasonably, and an olefin polymerization process by using this apparatus.
The term xe2x80x9cpolymerizationxe2x80x9d used in this specification means polymerization including homopolymerization and copolymerization; xe2x80x9cpolymerxe2x80x9d, polymer including homopolymer and copolymer.
2. Description of the Background
Olefin polymers are represented by polyethylene, polypropylene, and linear low density polyethylene, which is a copolymer of ethylene and xcex1-olefin, and the like. These olefin polymers are widely used for film-forming material and the like.
Such olefin polymers can be produced by using a Ziegler-Natta catalyst or a metallocene catalyst. In recent years, properties of transition-metal compound ingredients contained in this catalyst have been improved. As a result, an olefin-polymerization activity per unit weight of a transition metal has been greatly increased. Consequently, operation of removing catalysts after polymerization reaction can be excluded. On this account, cases adopting a gas phase polymerization, in which polymerization operation his easy, by using this highly active catalyst has been increased.
In the conventional gas phase polymerization, such a fluidized bed gas phase polymerization vessel (reactor) equipped with a gas-dispersing plate as shown in FIG. 12 has been much used. In the gas phase polymerization with use of this polymerization vessel, olefin or olefin-containing gas is introduced through an introducing pipe 72 into the bottom 70a of the polymerization vessel by using a compressor or a blower 73. Then, the above gas is uniformly dispersed through the gas-dispersing plate 79, risen up in the polymerization vessel and brought into contact with catalytic particles in a fluidized bed region 70b located on the upper side of the gas-dispersing plate 79. Consequently, polymerization reaction is progressed in a fluid state.
In this case, an olefin polymer is formed on each surface of the catalytic particles. Accordingly, solid particles each composed of the catalytic particle and olefin polymer are floated in the fluidized bed region 70b. And the polymer particles can be discharged outside out of a discharging line 75 to be recovered. On the other hand, olefin polymer particles polymerized in the fluidized bed region 70b tends to be scattered into the upper part of the fluidized region 70b. In order to prevent the particles from scattering, a reduction region 70c through a gas-circulating pipe 76 with large cross section is provided in the upper part of the fluidized bed polymerization vessel 70 for reducing a gas flow speed. Unreacted or unpolymerized gas is discharged from the top of the reduction region 70c, cooled by using a heat exchanger 77 with cooling water, brine or the like, and again, charged into the bottom 70a of the fluidized bed polymerization vessel 70. Thus, the unreacted or unpolymerized gas is reused by circulation.
By the way, when such fluidized bed polymerization reactor 70 as had aforementioned is operated for a long period of time in order to perform continuous gas phase polymerization, there is some case that the following results will be caused.
(1) In case that the dispersion of the solid particles in the fluidized bed region is not uniform, the solid particles will adhere to the inner wall of the fluidized bed polymerization vessel 70. When polymerization reaction is progressed in this state, heat of polymerization cannot be removed sufficiently from the adhered portion. Consequently, temperature will rise locally at this portion.
(2) Olefin polymer particles will weld together to grow up into mass or sheet polymers. These grown up particles will be dropped and settled in the bottom of the fluidized bed polymerization vessel 70. Otherwise, these particles stay in the middle part. Consequently, temperatures at these local spots will be lowered.
(3) Moreover, when polymerization reaction is progressed promptly within a short period of time, the inner temperature of the polymerization vessel 70 will rise quickly to make progress of polymerization at abnormal speed. Especially, when sudden reaction is locally occurred, hot spots will be generated. This will produce new sheet or mass polymers, thereby operation of the polymerization reactor 70 become unstable.
As for a monitoring means of these occurrence, as shown in FIG. 12, in the previous time, two temperature measuring devices 78a and 78b have been put into the fluidized bed region 70b of the fluidized bed polymerization vessel 70. Further, one temperature measuring device 78c has been put into the reduction region 70c. By these temperature measuring devices the inner temperatures of the fluidized bed polymerization vessel 70 have been checked. In other words, when something unusual in the temperatures, measured by these temperature measuring devices 78a, 78b and 78c such as unusual temperature rise, drop and the like, had been observed, operational conditions of the fluidized bed polymerization reactor 70 was changed for stabilizing polymerization state.
However when the temperature measuring devices 78a, 78b and 78c are located inside the fluidized polymerization vessel 70 by insertion for measuring the inner temperature thereof, the projected portion of a thermometer in the temperature measuring devices 78a, 78b and 78c will work as obstacle to convection of gas. Further, polymer particles will be adhered to and grown up on the temperature measuring devices 78a, 78b and 78c. Consequently, these polymer particles will be changed into sources of generating sheet or mass polymers. This will cause bad dispersion of the solid particles.
Namely, when many of the temperature measuring devices are arranged inside the fluidized bed polymerization vessel 70, this arrangement will invite residence of the solid particles around the temperature measuring device and lack of heat release, even though the solid particles in the fluidized bed region 70b are made to flow uniformly by dispersing uniformly fluid gas run into the gas introducing region 70a through the gas dispersing plate 79. Consequently, the solid particles will be adhered in a mass state to the inner wall of the fluidized bed polymerization vessel and the ratio of olefin particles welding together will increase.
Accordingly, such arrangement of the temperature measuring devices as had mentioned above, although it is indispensable to operation of the fluidized bed polymerization vessel, is inclined to cause non-uniform dispersion of the flowing solid particles, and also to cause instability of the fluidized bed. On this account, it is required to minimize the number of temperature measuring devices installed inside the polymerization vessel, especially, inside the fluidized bed.
However, the solid particles composed of catalytic particles and olefin polymer are floated in the fluidized bed region 70b so that the floated solid particles has their own distribution of temperatures, and positions at which heat spots appear are not fixed as well as their distribution is always changed. For that reason, it is very difficult to detect accurately the inner temperatures of the fluidized bed polymerization vessel 70. It is also very difficult to control exactly operational conditions of the fluidized bed polymerization vessel 70 based on this measurement.
As had mentioned above, the conventional temperature measuring method has disadvantages in that it is hard to detect speedily and exactly times and positions of heat spots occurring. Accordingly, it has been hitherto difficult to operate the fluidized bed polymerization vessel stably for a long period of time in succession.
Accordingly, the first object of the invention is to provide a fluidized bed polymerization apparatus for capable of arranging temperature measuring devices correspondingly to positions where heat spots appear without adhering polymer particles to each of the temperature measuring devices.
The second object of the present invention is to provide a fluidized bed polymerization apparatus in which a temperature measuring device capable of measuring the temperature of a polymerization vessel easily, for example on real time.
The third object of the present invention is to provide a fluidized bed polymerization apparatus capable of determining the state of polymerization progressing inside the polymerization vessel based on the measurement of the temperature measuring device, changing operational conditions and performing stable gas phase polymerization of olefin for a long period of time.
The fourth object of the present invention is to provide an olefin polymerization process in a gas phase stably for a long period of time by using the fluidized bed polymerization apparatus.
Other objects, feature and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings.
Namely, the present invention is related to a fluidized bed polymerization apparatus comprising:
(a) a fluidized bed polymerization vessel having a fluidized bed for polymerizing olefin as solid catalytic ingredient and polymer are fluidized by introducing olefin-containing fluid gas;
(b) a gas-circulating equipment for returning unreacted olefin-containing gas, which is streaming out from the top of the fluidized bed polymerization vessel, to the same polymerization vessel as well as controlling a circulating speed of the unreacted olefin-containing gas;
(c) a raw-material-feeding equipment for feeding fresh olefin to the fluidized bed polymerization vessel as well as controlling the feed of olefin;
(d) a catalyst-feeding equipment for feeding the solid catalyst into the fluidized bed polymerization vessel as well as controlling the feed of the catalyst;
(e) a temperature measuring device for measuring temperature or temperature distribution at plural different positions located on the external wall of the fluidized bed polymerization vessel; and
(f) a controlling means for controlling polymerization conditions based on the measurement with the temperature measuring device.
According to the present invention, the preferable temperature measuring device is made up of a plurality of temperature detectors. The plurality temperature detectors may be installed on the external wall of the fluidized bed polymerization vessel so as to keep contact with each other, or at roundabout position separating from the external wall to the extent of exerting no influence on a measuring accuracy, or in a cavity formed on the polymerization vessel enough to produce no projection on the inner wall surface of the polymerization vessel and to exert no influence on safety of equipment such as the mechanical strength of the polymerization vessel and the like; and a temperature measuring instrument for measuring the temperature inside the polymerization vessel indirectly through the temperature measuring device. Summing up, the temperature measuring device features to be arranged at a position capable of measuring the temperature inside the polymerization vessel indirectly and separately from the inner wall of the polymerization vessel. The temperature measuring instrument may have constitution capable of being arranged along the external wall of the polymerization vessel while height and direction are changed. This constitution makes it possible for the temperature measuring device to be arranged at positions corresponding to positions where heat spots appear without adhering polymer particles to the temperature measuring device.
As for the thermo-detector, it is preferable to use a thermoelectric thermometer having a thermocouple embedded in the head of a sheath. The head of the thermoelectric thermometer may be arranged and fixed on the external wall of the polymerization vessel while keeping contact with it. As for the fixing method, the following method may be employed: fixing the sheath head on the external wall of the polymerization vessel by welding; providing the external wall of the polymerization vessel with a stand for bolting having a female screw opening and pressing the sheath head on the external wall with the top of a bolt supported by the stand; making a small cavity on the external wall and embedding the sheath head into the cavity; or the like. Relating to fixing the thermo-detector, it is desirable to cover its periphery with thermal insulating material such as glass wool, rock wool and the like. The size of the thermal insulating material can be designed according to the circumstance.
Here, at least one of plural thermo-detectors to be fixed to the external wall of the polymerization vessel is desirably arranged at height of a distance of 0.1 to 1.5 times, preferably, 0.4 to 1.2 times as large as a value equal to the diameter in the fluidized bed region of the polymerization vessel, apart from a gas-dispersing plate upwardly. In case that the diameters of the fluidized bed region differ in accordance with its height, the value is a half of the sum of its maximum and minimum values. From the findings of the present inventors, the above position is the position liable to generate heat spots. Accordingly, it is desirable for ensuring stable operation to monitor the temperature inside the polymerization vessel by locating at least one of the thermo-detectors at the above position.
Another preferable temperature measuring device in the invention may be an infrared temperature measuring device capable of measuring temperature distribution on the external wall of the fluidized bed polymerization vessel. In this case, temperatures on some or all of the surface that the external wall of the fluid polymerization vessel has are measured by the infrared temperature measuring device from at roundabout position of the predetermined distance apart from the external wall of the fluidized bed polymerization vessel. Consequently, the measurement can be expressed by temperature distribution of the external wall. Especially, when the temperature distribution on each given section by partialization of the fluidized bed polymerization vessel""s external wall is measured at a position having the predetermined distance apart therefrom, temperature deviation in the polymerization vessel can be found instantly and easily.
By using this infrared temperature measuring device, temperature distribution can be measured of 2 to 40% by measurable area of the fluidized bed region, or the reduction region, or from the bottom to the middle of the fluidized bed region in the fluidized bed polymerization vessel. A driving mechanism of the infrared temperature measuring device can be provided, and temperature distribution can be measured of 2 to 100% by area for measuring of the peripheral surface of the polymerization vessel. A driving apparatus capable of moving the infrared temperature measuring device on a ring guide rail arranged around the polymerization vessel can be provided as a driving mechanism. Further, the infrared temperature measuring device may have an angle-variable means for fixing an angle variably in every direction in measuring as well as a zooming means for enlarging or reducing a measurable area of temperature distribution in the fluidized bed polymerization vessel.
In this invention, a means for controlling polymer conditions based on the above measurement is provided, thereby, stable operation of an polymerization apparatus is possible.
This controlling means can memorize at least one target value of temperature at corresponding measuring position or of temperature distribution, compare the target value with measured temperature or temperature distribution and calculate to change polymerization conditions so as to coincide with or approximate to the target value. Otherwise, there may be employed another method of memorizing a target value of temperature or temperature distribution on one or more of given sections each having the predetermined area for measuring by partialization of the external wall of the fluidized bed polymerization vessel followed by changing polymerization conditions in the same procedure as had aforementioned. This comparing-calculating steps may be performed by manual operation or automated operation. Especially, the latter case is preferable, since quick control is possible by storing the target value into the memory of a computing machine. The target value may be one value or values having range.
Change of polymerization conditions may be performed by a controlling process including: changing the supply of olefin charging into the fluidized bed polymerization vessel as well as the circulating speed of unreacted olefin-containing gas; changing the supply of the solid catalyst; changing the composition or the linear speed of flowing gas inside the polymerization vessel; changing the discharge amount of the olefin polymer from vessel so as to control the height of the fluidized bed in the vessel; or the like. An opening for supplying deactivated amount of catalytic ingredients may be provided through the fluidized bed polymerization vessel to control catalytic ingredients by supplying the deactivated amount thereof.
The present invention is also related to an olefin polymerization process by using a fluidized bed polymerization apparatus for comprising
(a) a fluidized bed polymerization vessel having a fluidized bed for polymerizing olefin as solid catalytic ingredient and polymer are fluidized by introducing olefin-containing gas for flowing,
(b) a gas-circulating equipment for returning unreacted olefin-containing gas, which is streaming out from the top of the fluidized bed polymerization vessel, to the same polymerization vessel as well as controlling a circulating speed of the unreacted olefin-containing gas,
(c) a raw-material-feeding equipment for feeding fresh olefin to the fluidized bed polymerization vessel as well as controlling the feed of olefin,
(d) a catalyst-feeding equipment for feeding the solid catalyst into the fluidized bed polymerization vessel as well as controlling the feed of the catalyst,
and comprising the steps of:
measuring temperature or temperature distribution at plural of different positions on the external wall surface of the fluidized bed polymerization vessel;
comparing the measured value with a target value of temperature or temperature distribution set beforehand correspondingly to one or more of measuring positions; and
changing polymerization conditions so as for the measured value to coincide with or approximate to the target value.